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A Preliminary Study on the Ornamentation Patterns of Ganoid Scales in Some Mesozoic Actinopterygian Fishes

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A Preliminary Study on the Ornamentation Patterns of Ganoid Scales in Some Mesozoic Actinopterygian Fishes See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/291973377 A preliminary study on the ornamentation patterns of ganoid scales in some Mesozoic actinopterygian fishes Article in Bollettino della Societa Paleontologica Italiana · December 2015 DOI: 10.4435/BSPI.2015.14 CITATIONS READS 0 206 2 authors: Claudio Garbelli Andrea Tintori Nanging Institute of Geology and paleontolo… University of Milan 14 PUBLICATIONS 36 CITATIONS 118 PUBLICATIONS 1,487 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Middle Triassic fishes across the Tethys View project All content following this page was uploaded by Andrea Tintori on 06 February 2016. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. TO L O N O G E I L C A A P I ' T A A T L E I I A Bollettino della Società Paleontologica Italiana, 54 (3), 2015, 219-228. Modena C N O A S S. P. I. A preliminary study on the ornamentation patterns of ganoid scales in some Mesozoic actinopterygian fishes Claudio GARBELLI & Andrea TINTORI C. Garbelli, Dipartimento di Scienze della Terra “Ardito Desio”, Università degli Studi di Milano, via Mangiagalli, 2, 20122 Milano, Italy; claudio. [email protected] A. Tintori, Dipartimento di Scienze della Terra “Ardito Desio”, Università degli Studi di Milano, via Mangiagalli, 2, 20122 Milano, Italy; andrea.tintori@ unimi.it KEY WORDS - Ganoid scales, basal actinopterygians, ornamentation, squamation pattern. ABSTRACT - Ganoid scales are one of the most common remains of vertebrates in the fossil record of Paleozoic and Mesozoic. Their knowledge is important for the understanding of the paleobiology and evolution of actinopterygian fishes. The distinctive feature of these scales is the outermost shiny layer of ganoine, an hyper-mineralized enamel-like tissue. During the Mesozoic, ganoid scales show a great variety of shapes and very different patterns of ornamentation made of ganoine. The surface of scales may be from smooth to very ornamented, with a relief arranged in tubercles, ridges, grooves or a combination of them. Here we present a preliminary study on the squamation of some Mesozoic non-teleost actinopterygians in order to test the association between body shape and ganoine ornamentation. Using several morphological descriptors, we built an empirical morphospace to compare ganoid scales ornamentation. The use of a quantitative method to describe scales allows to test if there is a meaningful correlation between body shape and ganoine ornamentation in non-teleost actinopterygians. We found an important association between body shape and scale ornamentation in the taxa under investigation. In particular, deep-bodied fishes bear a more complex and variegate ornamentation than fusiform ones. This finding has important implications in our understanding of non-teleost actinopterygians paleobiology. Since swimming activity is a primary function for fish and this is performed by the body acting as an integrated unit, the correlation between body shape and ganoine ornamentation could be related to hydrodynamics. A quantitative test of this hypothesis, however, would be desirable. RIASSUNTO - [Studio preliminare sugli schemi ornamentali delle scaglie ganoidi in alcuni pesci Attinopterigi del Mesozoico] - Le scaglie ganoidi sono uno dei più importanti e diffusi resti di vertebrati nel record fossile del Paleozoico e del Mesozoico. La loro conoscenza è importante per capire la paleobiologia e l’evoluzione dei pesci Attinopterigi. Il carattere distintivo di queste scaglie è la copertura esterna che è costituita dalla ganoina, un tessuto iper-mineralizzato simile allo smalto. Nel Mesozoico, le scaglie ganoidi sono estremamente differenziate e mostrano quindi una grande variabilità di forme e ornamentazioni prodotte dalla ganoina. La superficie delle scaglie può essere da liscia a fortemente ornata, con un micro-rilievo organizzato in tubercoli, creste, scanalature e dentellature, od una combinazione di essi. In questo lavoro abbiamo studiato le scaglie di alcuni Attinopterigi non-teleostei del Mesozoico, per verificare se esiste una relazione tra la forma del corpo e l’ornamentazione prodotta dalla ganoina. Utilizzando alcuni descrittori morfologici, abbiamo costruito un morfospazio empirico per confrontare le scaglie in termini di morfologia ed ornamentazione. L’uso di un metodo quantitativo per descrivere le scaglie ha permesso di verificare se c’è una correlazione significativa tra la forma del corpo e l’ornamentazione delle scaglie nei pesci Attinopterigii non-telostei. Abbiamo trovato un’associazione importante tra forma del corpo e descrittori morfologici delle scaglie nei casi studiati. In particolare, i pesci cosiddetti “deep-bodied” possiedono un’ornamentazione delle scaglie più complessa e differenziata di quella delle specie fusiformi. Questa osservazione ha delle importanti implicazioni per la nostra comprensione della paleobiologia dei pesci Attinopterigi non-teleostei. Infatti, siccome l’attività del nuoto è una funzione primaria per i pesci ed è attuata dall’organismo come se il corpo fosse un’unità integrata, la correlazione tra forma del corpo e ornamentazione della ganoina potrebbe essere relazionata all’idrodinamica. In futuro, un test quantitativo per verificare questa ipotesi sarebbe auspicabile. INTRODUCTION potentially provide flexural constrains (Gemballa & Bartsch, 2002). The ganoid scales are a synapomorphic groundplan During the Paleozoic and Mesozoic and before the feature of ray-finned fishes, the Actinopterygii (Schultze, vast teleostean radiation, ganoid scales were the common 1977; Patterson, 1982), and these structures showed a type of body covering among lower actinopterygians much greater amount of variability in deep time. Today, and their morphology was greatly variable, if compared only Polypteridae and Lepisosteidae retain ganoid scales with the scales of Polypteridae and Lepisosteidae (e.g., and their study allowed biologists and paleontologists Trinajstic, 1999a, b; Chen et al., 2012). This variability to clarify morpho-functional aspects of this kind of encompasses features such as the general shape of “exoskeleton”. Ganoid scales of these modern groups scales and the microrilief of ganoine covering, usually have several functional implications for swimming, such called “ornamentation”. Compared to the homogeneous as enhanced station-holding (Webb et al., 1992), control aspect of modern ganoid scales, primitive groups of of body stiffness and undulatory wave motion during actinopterygians show a much higher variability in terms steady swimming (Long et al., 1996); these are designed of scales shape and ornamentation of ganoine. The scales to permit extreme body curvatures in spite to the rigid from fossil record exhibit a rhomboid to very elongate structure of ganoid scales in the basal actinopterygian outline, from subcircular to squared. Their posterior fishes, structured with peg-and-socket articulation, which margin may be from smooth to serrated and their surface ISSN 0375-7633 doi:10.4435/BSPI.2015.14 220 Bollettino della Società Paleontologica Italiana, 54 (3), 2015 may be from smooth to highly ornamented, with a a complete ganoid squamation were investigated: microsculpture composed of longitudinal or transversal Paralepidotus ornatus Agassiz, 1843 (according to Tintori, ridges, isolated tubercles, crests and grooves. The meaning 1996); Gabanellia agilis Tintori & Lombardo, 1996; of these characters is not fully understood and some Stoppania gaetanii Lombardo et al., 2008; Felberia excelsa speculative hypotheses were proposed, mainly involving Lombardo & Tintori, 2004; Endennia licia Lombardo & functions related to swimming (Aleyev, 1977). One of the Brambillasca, 2005; Semiolepis brembanus Lombardo & most widespread ideas is that the surface roughness of fish Tintori, 2008; Dapedium politum Leach in De La Beche, skin may have some hydrodynamics functions related to 1822; Dapedium noricum Tintori, 1983; Sargodon tomicus delaying the boundary layer separation or to the reduction Plieninger, 1847; Ptycholepis gracilis Davis, 1884; of skin friction drag (Fletcher et al., 2014). The boundary Ptycholepis bollensis Agassiz, 1833; Eugnathus philpotae layer separation can easily occur across smooth surfaces Agassiz, 1843; Luoxiongichthys hyperdorsalis Wen et in regions of adverse pressure gradient, but experimental al., 2012; Allolepidotus bellottii De Alessandri, 1910; measures suggest that there is no separation (Anderson Bobasatrania sp. White, 1932; Asialepidotus sp. Su, 1959. et al., 2001). The scales with ridges and grooves may Specimens belonging to these taxa were selected possibly promote the formation of microflows (Sudo et for study on the basis of quality preservation of their al., 2002). This could be consistent with the generation squamation pattern and scale morphology. The selected of a turbulent boundary layer in which the separation is specimens are deposited in the following museums: delayed, if compared to a laminar boundary layer. Some Museo di Paleontologia del Dipartimento di Scienze della authors argued that ganoine ornamentation could have Terra“ A. Desio”, Università degli Studi di Milano, Italy performed this function in extinct fishes (Burdak, 1986). (acronym MPUM); Museo Civico di Storia
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